Being tired for months while your health check comes back normal is a common combination. There is a reason for it.
This article answers three things. How you find out whether you are anaemic, whether iron tablets alone will fix it, and how much to take for how long. The screening items come from Korea's National Health Insurance Service, diagnosis and treatment from the US National Heart, Lung, and Blood Institute (NHLBI) and the NIH Office of Dietary Supplements (ODS), and prevalence from Korea's Disease Control agency and the WHO.
The national health check measures one thing: haemoglobin
This is the answer to “normal results, still exhausted.” Korea's National Health Insurance Service lists its screening items as pairs of “target condition → test”, and the anaemia row reads like this.
| Target condition | Test performed |
|---|---|
| Anaemia | Haemoglobin |
| Obesity | Height, weight, waist circumference, BMI |
| Hypertension | Blood pressure |
| Diabetes | Fasting glucose |
| Kidney disease | Urine protein, serum creatinine, eGFR |
| Liver disease | AST, ALT, γ-GTP |
| Tuberculosis and chest conditions | Chest X-ray |
| Vision and hearing | Visual acuity, hearing |
| Oral health | Dental examination |
“Anaemia” appears as a target condition in its own right, and the test against it is haemoglobin alone. The difficulty is that anaemia was never a one-test question. The NHLBI lists four.
| Test | What it shows | In the national check? |
|---|---|---|
| Full blood count | Red cells generally | No |
| Haemoglobin | How well your blood carries oxygen right now | Yes |
| Serum iron | Iron in the blood (below 10 micromoles/L is low) | No |
| Ferritin | Iron held in storage (below 10 micrograms/L is low) | No |
Haemoglobin and ferritin measure different things. Haemoglobin is the blood circulating now; ferritin is what remains in the warehouse. There is a stretch where the stores are draining while the blood still holds up — and during it, the screening report prints “normal.”
So if the tiredness persists after a normal result, it is worth considering that only haemoglobin was measured. Seeing the stored iron means asking for a ferritin test through a doctor.
Screening intervals differ by insurance category: every two years for regional subscribers, dependants and office-based employees, and every year for non-office employees. Reading the other numbers on the report is covered in the results sheet article.
How common is it — women peak in their thirties
From Korea's National Health and Nutrition Examination Survey:
| Group | Anaemia prevalence |
|---|---|
| All, aged 10 and over | 8.8% |
| All, aged 30 and over | 10.7% |
| Urban | 8.8% |
| Rural | 8.8% — no difference |
What matters is the distribution by sex and age, and the two curves have completely different shapes. Women peak at 30–39, with 19–29 and 50–59 next, and the teenage figure is already not low. Men show almost nothing when young and climb sharply at 60–69.
The same word covers reproductive years for women and old age for men. Why menstrual blood loss sits at the centre of this article is visible in that distribution. By income, prevalence also runs clearly higher in lower brackets.
The sex-age and income figures are presented only as bar charts, so no values are quoted from them. The shapes above are read from the charts; the only citable numbers are the four rows in the table.
It is common globally too. For 2019 the WHO reports anaemia in 30% of non-pregnant women aged 15–49 (539 million) and 37% of pregnant women in the same range (32 million), naming “iron deficiency, mainly from inadequate dietary iron intake” as the most common cause. Global figures cannot be set beside Korea's 8.8%, but they do retire the thought that you alone are unusually tired.
Symptoms — there may be none
The NHLBI puts one sentence ahead of its symptom list.
“If your anaemia is mild, you may not have any symptoms.”
“Symptoms of anaemia can come on quickly or slowly, depending on the cause.”
— US National Heart, Lung, and Blood Institute, anaemia symptoms
| Source | Symptoms listed |
|---|---|
| Anaemia generally | Weakness, pallor, fatigue, feeling cold, shortness of breath, headache, dizziness and fainting, bleeding, jaundice |
| Iron deficiency anaemia | Fatigue, shortness of breath, chest pain, dizziness or light-headedness, cold hands and feet, pale skin |
| Low iron (ODS) | Upset stomach, weakness, fatigue, lack of energy, problems with concentration and memory |
| Left untreated | Restless legs syndrome may develop |
The line worth noticing is the ODS entry on concentration and memory. Tiredness is easy to register; a head that will not work properly is rarely connected to iron.
When iron tablets are not the answer
The main route to iron deficiency in women is menstrual blood loss, and it is easy to file under “I've always been heavy.” The NHLBI is direct about it.
“Anaemia from losing too much blood during your period is not normal.”
The warning signs given are “having to change a tampon or pad within two hours” and “passing large blood clots.”
— US National Heart, Lung, and Blood Institute, anaemia causes and risk factors (updated 18 December 2025)
Past that line, the next step is not buying supplements but having the bleeding looked into. Topping up the iron leaves the leak where it is.
Bleeding is not the only risk factor.
| Risk factor | NHLBI wording |
|---|---|
| Blood loss | Heavy periods, bleeding in childbirth, other blood loss |
| Diet | “People who lack iron, vitamin B12 or folate are at higher risk” |
| Age | “The chance of developing anaemia rises with age” |
| Family history | A family history of inherited anaemia |
| Other conditions | Chronic kidney disease, inflammation from infection, cancer, autoimmune disease |
| Lifestyle | Heavy drinking |
Chronic kidney disease on that list is worth noting: if anaemia keeps returning without an obvious cause, it belongs among the things to check.
Once you start, it runs three to six months
This is where practice diverges most. Iron is not a few days' course you stop when your energy returns.
“Iron supplements … are the most common treatment, and it takes three to six months to restore your iron levels.”
Side effects listed are “a metallic taste, vomiting, diarrhoea and constipation,” with the advice that taking them with food or adjusting the dose may help.
— US National Heart, Lung, and Blood Institute, iron deficiency anaemia
Feeling better and refilling the stores happen at different times. When to stop is decided by a repeat test, not by how you feel.
How much, and what to take it with
The requirement more than halves at menopause.
| Group | Daily recommendation (ODS) |
|---|---|
| Women 19–50 | 18mg |
| Pregnancy | 27mg |
| 51 and over | 8mg |
| Adult men | 8mg |
| Upper limit (19 and over) | 45mg |
Vegetarians need a second look. The ODS states that “vegetarians who do not eat meat, poultry or seafood need almost twice as much iron”, because non-haem iron absorbs poorly. Being both vegetarian and of reproductive age stacks the two conditions.
And what you take it with changes how much you absorb.
| Direction | ODS wording |
|---|---|
| Improves absorption | Meat, poultry and seafood, and foods containing vitamin C — citrus, strawberries, peppers, tomatoes, broccoli |
| Reduces absorption | Calcium, and certain medicines |
| Acid reducers | “Proton pump inhibitors reduce non-haem iron absorption” |
| Thyroid medication | “Iron interferes with the absorption of levothyroxine” |
| Parkinson's medication | “Iron reduces the effectiveness of levodopa” |
Swallowing a calcium tablet and an iron tablet together is a common routine — calcium for bones, iron for the tiredness. If you take both, spacing them apart is better (see calcium and vitamin D). If thyroid medication is in the mix, see the thyroid article too, and confirm the order with whoever prescribed it.
Questions people ask
I'm exhausted but my screening was normal
The screening measured haemoglobin only. Ferritin, which shows stored iron, is not in the national programme. There is a stretch where the stores drain while the blood still holds, so if symptoms persist, ask for a ferritin test.
Isn't anaemia haemoglobin below 12 g/dL?
The figure is widely used, but it appears in neither the WHO fact sheet nor the NHLBI pages we read. The WHO says only that thresholds are “set by age, sex and physiological status” and defers the values to separate guidelines. So no number is given here. Use the reference range printed on your own report.
Will iron tablets alone fix it?
Not if heavy periods are the cause. The NHLBI states that “anaemia from losing too much blood during your period is not normal” and flags changing protection within two hours or passing large clots. The leak has to be addressed first.
Iron upsets my stomach
The NHLBI lists metallic taste, vomiting, diarrhoea and constipation as side effects and suggests taking them with food or adjusting the dose. Try that conversation before stopping on your own.
I don't eat meat — is that a problem?
On ODS figures you need almost twice as much. With only non-haem iron available, pairing it with vitamin C foods matters more.
Is more always better?
No. The ODS fixes the upper limit for adults at 45mg, and as above, iron can interfere with other medicines.
Sources
- Korea National Health Insurance Service — general health screening guidance (checked August 2026). Source for the full set of “target condition → test” pairs (anaemia → haemoglobin, obesity → height, weight, waist and BMI, hypertension → blood pressure, diabetes → fasting glucose, kidney disease → urine protein, creatinine and eGFR, liver disease → AST, ALT and γ-GTP, tuberculosis and chest conditions → chest X-ray, vision and hearing, oral health → dental examination) and for the eligibility categories and intervals.
- US National Heart, Lung, and Blood Institute — iron deficiency anaemia. Source for the four tests (full blood count, haemoglobin, serum iron, ferritin), serum iron of 10–30 micromoles/L and ferritin below 10 micrograms/L, “three to six months to restore your iron levels,” the side effects, restless legs syndrome, and iron-rich foods.
- US National Heart, Lung, and Blood Institute — anaemia causes and risk factors (updated 18 December 2025) and anaemia symptoms. Source for “anaemia from losing too much blood during your period is not normal,” the two-hour and large-clot warning signs, the risk factor list including chronic kidney disease, and “if your anaemia is mild, you may not have any symptoms.”
- NIH Office of Dietary Supplements — iron. Source for 18mg for women 19–50, 27mg in pregnancy, 8mg from 51, the 45mg upper limit, “vegetarians need almost twice as much iron,” improved absorption with vitamin C and meat, interference from calcium, the interactions with proton pump inhibitors, levothyroxine and levodopa, and “problems with concentration and memory” as a sign of low iron.
- Korea Disease Control and Prevention Agency — National Health and Nutrition Examination Survey, anaemia prevalence (2023). Source for 8.8% among those aged 10 and over, 10.7% from age 30, the identical 8.8% in urban and rural areas, the definition, and the shapes of the distributions by sex, age and income. The latter are published only as bar charts, so no values are quoted.
- World Health Organization — anaemia fact sheet (February 2025). Source for 30% of non-pregnant women aged 15–49 (539 million) and 37% of pregnant women (32 million) in 2019, for iron deficiency as the most common nutritional cause, and for thresholds being set by age, sex and physiological status.
- What we read into it. “The screening only sees haemoglobin, so stored iron is unknown” comes from setting the Insurance Service's test list beside the NHLBI's four tests; no source frames it that way. Korea's 8.8% and the WHO's 30% cannot be compared directly — different populations and years (all aged 10 and over in 2023 against women aged 15–49 globally in 2019). And how much of Korea's 8.8% is iron deficiency specifically is not in the indicator.
Where to check further
This article goes as far as the agency material allows. The rest is best looked at here.
- Whether your haemoglobin is normal — checked here, on your own report. Neither the WHO nor the NHLBI publishes a threshold figure, so none appears here. The reference range printed alongside your result is what decides it. Past reports can be pulled up through Government24’s screening-results service or the Service’s own portal.
- Ferritin — request it through a doctor. It is not a national screening item, and the NHLBI goes only as far as “below 10 micrograms/L is low.” What counts as sufficient varies by laboratory. The Korean explanation sits on the Disease Control agency’s national health information portal.
- How long to keep taking iron — decide it by retesting. Three to six months is how long restoration takes; the actual stopping point should follow a repeat measurement. A retest sits outside the standard screening panel, so it has to be requested.
As of August 2026. Screening items come from the National Health Insurance Service, diagnosis and treatment length from the NHLBI, amounts and interactions from the ODS, and prevalence from Korea's Disease Control agency and the WHO. As iron requirements fall after menopause, bone health takes on more weight — see the menopause transition. This is general health information and does not substitute for medical diagnosis or treatment. If bleeding is suspected or symptoms persist, see a doctor.
